I have a 2004 MINI Cooper S. BMW picked up the MINI project in the late '90s when they bought Rover Group. From what I've read they pretty much re-engineered the Rover effort from the ground up, using a lot of suspension design and infrastructure (wiring, etc) from various generations of the 3-series. The engine is sourced from a Brazilian Chrysler-BMW joint venture...I was bothered by this when I first heard about it but then remembered that prior to DCX, Chrysler made some pretty solid if unsophisticated four cylinder motors.
I really love the car overall. The biggest PIA factor is the lack of cargo space, but that wasn't a surprise. Driving-wise, my biggest complaint is the lack of a limited-slip and the resulting inside-wheel spin upon corner exits. Of course, you can now spec an LSD from the factory, something you couldn't do in April 2004.
The build quality of later models (mid-2003 and later) is much improved over the early cars, which had a number of issues. From my experience and what I've heard from others, just about all those bugs have been ironed out. I've had very few problems with mine, none of which were "leave-you-stranded" issues...mainly interior rattles, weak hatch struts, and a broken baffle in the exhaust. This is over 25k daily-driven miles since May 2004, including one track day.
I respectfully disagree with Schnell540 on the interior design. My first impressions upon visiting the MINI dealer in March 2002 were the same as his--form over function, not purposeful, etc. However, upon living with it I have come to realize that the design is actually very smart, very efficient and very conducive to fast driving. The materials quality isn't superior (read: VW) but for the price point, it's OK.
On the whole, I would go so far as to say the impression that the MINI is all marketing is one held by folks who haven't spent enough time behind the wheel. It isn't a 5-series and it doesn't pretend to be...it is an exceptionally well engineered front-wheel-drive hatchback.
Go drive one and you'll know pretty quickly whether it's your cup of tea or not.

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Tim L.
whisperbomb at gmail dot com
2004 MINI Cooper S
2006 Subaru Outback 2.5i